This invention relates to a grinding machine to grind a tool to a predetermined shape to cut a desired shape into a piece of wood by first engaging the grinding wheel with the tool in the face-up position.
The process of making a woodworking tool, such as a knife or the like, to cut a given shape in a piece of wood involves two basic steps: making a template having the exact shape as the wood product; and grinding the front of the knife in the face up position. However, since the angle at which the knife strikes the wood varies as the depth of cut changes, the exact shape desired to be cut into the wood cannot be ground into the knife. Accordingly, such factors as the depth of the cut to be made and the angular relationships of the knife relative to the wood during the cutting process must be taken into account. Therefore, the knife is ground with a deeper contour than that of the template or the piece of wood, because the knife is disposed at an angular relationship in the cutterhead relative to the wood. The apparatus of this invention automatically scribes the elongation in the knife. Prior art devices such as U.S. Pat. No. 1,395,145 disclose grinders that make use of a template, but fail to automatically take into account the elongation necessary when cutting the knife blank. A special template has to be prepared for machines of this type. There is no adequate ability in this type of machine to rotate the knife blade in relation to the grinding wheel in order to produce the required pattern elongation.
Because of the angular relationships between the knife and the piece of wood in the prior art a template had to be experimentally designed by hand so that the machine would grind the knife to cut the desired shape in the wood, and the template did not have the same shape as the desired shape of the wood. This present device automatically calculates the error caused by the knife being held in the off center position in the cutterhead. Thus the profile of the wood and the template are identical. The present apparatus allows the operator to view the template and the upper face of the tool being ground at the same time and in an identical face up relationship, not a mirror image as in other prior art. This is accomplished by mounting the cutting tool or knife blade onto the tool holder with the knife face up. The tool holder is then placed on a workshaft, it then being mounted on bearings on top of support devices. A counterweight, when lifted off a support, is locked in a higher position by turning the counterweight clockwise which makes the counterweight arm and work arbor holding the knife support move as one unit. The downward weight rotates the knife under a guide finger to change the angle of grind as you go deeper into the pattern. It allows you to blend your grinding clearance caused by the knife being held in the cutterhead in the off center position. If the knife face was on the same centerline of the cutterhead you would not need to stretch the knife profile. Ninety-nine percent (99%) of all woodworking tools incorporate the off center principle. Hence the elongated pattern has to be ground in the knife. The greater the off center, the greater the elongation needed.
The relationship of the template and pin relative to the knife results in the knife actually moving a greater distance than the actual depth of cut to be made in the wood and the knife is accordingly ground deeper than the actual depth of the template, which the guide pin follows. Accordingly, the knife is automatically ground to the desired shape to compensate for the difference in angle of the knife relative to the piece of wood as the depth of cut changes, and the exact shape to be formed is therefore easily obtained without requiring time consuming and complicated hand design methods.
In the present invention the template is viewed along with the knife in a face-up position by the operator, this being the identical position its mounted on the cutterhead spindle. The operator does not have to view the knife face-down as in the other prior art devices, which would present the knife and the template in mirror image relationship.